Oxide and carbide ceramics have many desirable properties which are most useful, and indeed required, for many modern industrial and technological uses and processes. These desirable properties include very high hardness, light weight, abrasion resistance, stability and retention of properties at high temperatures, chemical durability and inertness. Their brittleness characteristic, however, often limits their use when structural integrity in cyclic load and stress conditions exist or are required.
A world-wide market has developed for silicon carbide for a variety of structural, abrasive and electronic applications. Boron carbide, another commonly-used ceramic, is widely used in abrasion and wear applications. It is also a major component in nuclear applications because of its capability to capture neutrons. When used alone, these ceramics exhibit the undesirable characteristics described above; namely, the lack of strength and toughness.
In recent years there has been increasing interest in the manufacture of composite materials utilizing ceramic whiskers, fibers or platelets as the material used for reinforcing metallic, polymeric or ceramic matrix materials. This not only strengthens most metallic and polymeric matrix materials, but also provides an attractive toughening mechanism for ceramics.
Various composites have been described in the patent literature, some of which are U.S. Pat. No. 4,370,390 issued to R. Burk on Jan. 25, 1983; U.S. Pat. No. 4,461,842 issued to J. Jamet on Jul. 24, 1984; U.S. Pat. No. 4,543,345 issued to G. Wei on Sep. 24, 1985; U.S. Pat. No. 4,558,016 issued to S. Bronson et al on Dec. 10, 1985; U.S. Pat. No. 4,585,500 issued to L. Minjolle et al on Apr. 29, 1986; and U.S. Pat. No. 5,162,270 issued to P. Ownby et al on Nov. 10, 1992.
Other research on reinforced composites has been disclosed in U.S. Pat. No. 3,520,740 issued to A. Addamiano on Jul. 14, 1970; U.S. Pat. No. 3,011,877 issued to H. Schwieckert et al on Dec. 5, 1961; U.S. Pat. No. 4,387,080 issued to Hatta et al on Jun. 7, 1983; and U.S. Pat. Nos. 3,174,827 and 3,230,053 issued to N. Wakerlyn et al on Mar. 23, 1965, and Jan. 18, 1966, respectively. Recent work regarding the strengthening of metallic composites is described in co-pending U.S. patent application Ser. No. 08/467,188 filed May 6, 1995, with a common inventor and assignee to the present invention.
Many, if not most, of the materials used for strengthening of ceramics often add undesired weight to the ceramic composite. For example, the typical carbide-type strengthening agents when added to aluminum oxide in any significant amount can have an effect upon some of the uses of the ceramic body.
Accordingly, it is an object of the present invention to provide a strengthening and toughening agent for ceramic bodies that reduces the weight of the added reinforcement material.
Another object of the present invention is to provide a strengthening and toughening agent for ceramic bodies in the form of silicon hexaboride.
A further object of the present invention is to provide a strengthening and toughening agent for ceramic bodies in the form of Si-B-C.
These and other objects of the present invention will become apparent upon a consideration of a detailed description that follows.